1. Field of the Invention
The present invention relates to a lens barrel that collapses, stores lens groups therein when not in use, and extends the lens groups to predetermined positions when photographing. More particularly, the present invention relates to a lens barrel, a camera, and a portable information terminal apparatus including a lens barrel suitable for a zoom lens unit that can change the focal distance by relatively moving a plurality of lens groups.
2. Discussion of the Background
With improvement in high performance of a photographing lens such as a zoom lens unit that is capable of changing the focal distance and in downsizing according to the user's demand as to an image pickup apparatus such as a digital camera, there are increasing types of image pickup apparatus employing a so-called collapsing photographing lens unit in which lens cylinders are stored within a body of the image pickup apparatus when photographing is not carried out. Furthermore, since not only simple reduction in dimensions, but also further reduction in thickness of the image pickup apparatus are also demanded, it is now important to reduce the thickness of the lens barrel portion in a collapsed state to the minimum limit.
As a technology to cope with the demand for reduction in thickness of the image pickup apparatus, a collapsible construction has been used, in which the lens cylinders are stored into the body of the image pickup apparatus when the photographing is not carried out and in which a part of the lenses is evacuated from an optical axis of the lenses in photographing, when the lens cylinders are collapsed and stored. Such a technology is disclosed, for example, in JP-A 2003-315861 and in JP-A 2003-149723. According to the structures disclosed in these Japanese unexamined patent application publications, since a part of the lenses is evacuated from the optical axis when the lens cylinders are stored, the dimension of the entire lenses in a direction of the optical axis can be reduced in the collapsed state, so that the thickness of the image pickup apparatus can be reduced.
However, in the structures disclosed in JP-A 2003-315861 and JP-A 2003-149723, the position of the lens evacuated from the optical axis is substantially within that lens cylinder which has the maximum outer diameter. Therefore, the lens cylinders contribute to reduction in thickness of the image pickup apparatus when the lenses are stored, but the outer diameter of the lens barrel increases. When compared with a case where the lens is not evacuated from the optical axis, since the outer diameter of the lens cylinders increase, the dimensions of the lens cylinders, in particular, the dimensions of the lens cylinders as viewed in a plane orthogonal to the optical axis increase. As a result, there arises a problem that the dimensions of the image pickup apparatus, in particular, the dimension as viewed from a front side of the image pickup apparatus increases.
On the other hand, in a lens barrel in which some of the lenses are evacuated from the optical axis when the lens barrel is stored, if an external impact is applied to the lens barrel as in a case of unintentional drop of a camera, a portable information terminal, or the like including the lens barrel, or collision of the camera, the portable information terminal, or the like against another object, a lens frame of the lens barrel at an object side is forced into a collapsed state when the lens to be evacuated is on the optical axis. This causes a specific problem of making the retractable lens retaining frame subject to damage.